1. Field of the Invention
The present invention relates generally to an electronic torque hand tool, and more particularly to an electronic torque wrench with early-warning function.
2. Description of the Related Art
A conventional electronic torque wrench generally has torque warning function. A user can set a torque warning value according to the necessary tightening torque for different threaded members. When the operation torque of the wrench reaches the torque warning value, the wrench will give a warning to remind the user that the operation torque has reached the set torque value and he/she should stop wrenching the threaded member so as to avoid over-tightening thereof.
However, inertia will take place when operating and applying a force to a hand tool. Therefore, when the user finds the warning or reminder, the user often fails to immediately stop wrenching the threaded member and will further wrench the threaded member with the wrench for a short period of time. Under such circumstance, the inertial application force will lead to extra torque applied to the threaded member and the operation torque of the wrench may exceed the necessary tightening torque for the threaded member. As a result, the threaded member will be over-tightened by error.
In order to solve the problem that the inertial application force will cause the real tightening torque is greater than the necessary/set tightening torque for the threaded member, the applicant's U.S. Pat. No. 9,283,663 has disclosed an electronic torque wrench, according to the electronic torque wrench, a user can set a torque warning value lower than the necessary tightening force for the threaded member. Therefore, the real tightening torque will not exceed the necessary tightening force for the threaded member after the force is inertly applied to the threaded member. This solves the problem caused by the inertial application force.
The above patent can truly solve the problem caused by the inertial application force, however, such electronic torque wrench is still not optimal. This is because the affection of the inertial application force on different threaded members necessitating different tightening torques is varied. For a threaded member necessitating greater tightening torque, after the force is inertly applied to the threaded member, the tightening force is relatively unlikely to exceed the necessary tightening force. However, for a threaded member only necessitating small tightening torque, after the force is inertly applied to the threaded member, the tightening force is easy to exceed the necessary tightening force.
Therefore, with respect to a threaded member only necessitating small tightening torque, a user is still hard to stop wrenching the threaded member in a very short time to avoid over-tightening.
It is therefore tried by the applicant to provide an electronic torque wrench with early-warning function. Moreover, the extent to which the early-warning is made earlier is varied with different threaded members necessitating different tightening torques so as to solve the above problem.